The present invention relates to a tool for removing pins from bores in plates. The invention has particular application to the removal from the upper core plate of a nuclear reactor, remnants of split pins used to anchor guide tube assemblies.
A nuclear reactor typically includes a reactor vessel having a reactor core disposed between lower and upper core plates. The core includes a fuel rod assembly comprising a plurality of fuel rods which are lowered into place through corresponding apertures in the upper core plate. In order to guide the fuel rod insertion, guide tube assemblies are utilized, each being supported on an upper support plate disposed near the upper end of the vessel. Each guide tube assembly extends down to the upper core plate and has a bottom plate disposed for seating in the corresponding aperture in the upper core plate, this bottom plate carrying a pair of anchoring split pins which are respectively frictionally received in corresponding anchor bores on opposite sides of the seating aperture. The upper end of each guide tube assembly is received through a large hole in the upper support plate. The reactor also includes a plurality of support columns, thermocouples and the like which are also disposed between the upper core plate and the upper support plate and which, along with the guide tube assemblies, form what is known as the "upper internals" of the reactor.
In refueling of the nuclear reactor, it is necessary to remove the spent fuel rods from the core and replace them with new fuel rods. Before the spent fuel rods can be removed, the guide tube assemblies must first be removed. Commonly, the metal in the split pin tends to harden as a result of the alternating heat and cold of the reactor cycles, thus making the pins brittle and subject to breakage. Thus, when the guide tube assemblies are pulled, the force necessary to pull the split pins from their bores frequently results in their breakage, leaving pin remnants in the bores. These broken split pins are replaced on the guide tube assemblies, but before the guide tube assemblies can be reinstalled, the old split pin remnants must be removed from the upper core plate. This removal is complicated by the fact that the upper core plate is between 30 and 60 feet beneath the work platform or bridge from which the removal operation must be performed, and by the fact that the reactor vessel is filled with water. Furthermore, the upper support plate obscures the upper core plate, so that it can be viewed only through the holes in the upper support plate. Finally, the pin remnants cannot be simply punched down out of their bores, since they would then fall into and foul the reactor core.